The Sinister Face of Tuberculosis

Figure 2b :High resolution images of the lung window showing miliary nodules in bilateral upper lobes.

Discussion

Tuberculosis is an infectious granulomatous disease caused by Mycobacterium tuberculosis, an acid-fast bacillus that is transmitted primarily via the respiratory route. Usually the primary focus is lungs and then the disease spreads secondarily to other organs. The disease may manifest as primary TB in children or become latent and then get reactivated in later life as post primary TB.

It is recognized that primary TB is primarily seen in children and presents either as mediastinal lymphadenopathy, parenchymal consolidation without upper lobe predilection / cavitation or as miliary TB and pleural effusion. In contrast, post primary is classically seen in adults, is more infectious, associated with upper lobe cavitation and absence of significant mediastinal lymphadenopathy. Although historically, these forms are distinct with unique clinical and radiological features, rarely overlapping characteristics between the two forms may be discernable.

TB is uncommon in adolescents and differs substantially from disease in younger children as they are more likely to be infectious and present symptomatically [1]. Clinical and radiographic findings may however mirror those of adults, with reactivation disease in lung apices [2], or of younger children, with intrathoracic adenopathy and higher rates of extrapulmonary disease than seen in adults [3]. Thus it may be often difficult to differentiate primary or post primary TB in adolescents as they may have common characteristics features of both.

Miliary disease is form of primary tuberculosis and traditionally has been observed more commonly in primary than post-primary disease. It is often observed in the immunocompromised individuals and generally has extra-pulmonary involvement. Among immunocompetent adults, miliary TB accounts for fewer than 2 per cent of all cases of TB [4-6]. Historically, miliary TB was considered a disease of infants and children, however currently, two peaks are evident, first in adolescence and young adults and second in elderly [4-6]. The inadequacy of effector T-cell response in containment of M. tuberculosis is considered responsible for progression to miliary TB, representing the Th2 end of spectrum [7- 8]. Conversely, cavitation occurs secondary to caseation necrosis and is a marker of body’s effective T- cell immune response, representing the Th1 end of spectrum. Cavitation in pulmonary TB represents reactivation of disease, as in post-primary tuberculosis [9,10]. Our immunocompetent patient had simultaneous occurrence of cavitatory lesions, miliary and mediastinal lymph-nodal tuberculosis, which represents a continuum of both primary and post-primary TB.

Host immune response status may be a better predictor of radiographic findings than classification by primary and post-primary TB [11]. It is important to emphasize that although cavitation, upper lobe involvement and sputum positivity are predominantly seen in post-primary TB, they may rarely be signs of active primary TB [11]. Infrequently, endobronchial spread in cavitatory TB may lead to air-space consolidation and diffuse parenchymal infiltrates typical of primary TB. In fact, quite unexpectedly, a recent study has demonstrated occurrence of upper lobe predilection and cavitation in healthy adolescents diagnosed with primary TB [12].

Learning points

1. A high index of suspicion is required for diagnosing tuberculosis in adolescents.
2. Simultaneous existence of miliary, mediastinal lymph-nodal and pulmonary tuberculosis cavitary lesions is very rare.
3. High endemicity of tuberculosis in India and malnutrition may be responsible for this unusual presentation

References

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